Radiolucent 4D Ultrasound Imaging: System Design and Application to Radiotherapy Guidance

Abstract

Four-dimensional (4D) ultrasound (US) is an attractive modality for image guidance due to its real-time, non-ionizing, volumetric imaging capability with high soft tissue contrast. However, existing 4D US imaging systems contain large volumes of metal which interfere with diagnostic and therapeutic ionizing radiation in procedures such as CT imaging and radiation therapy. This study aimed to design and characterize a novel 4D Radiolucent Remotely-Actuated UltraSound Scanning (RRUSS) device that overcomes this limitation. In a phantom, we evaluated the imaging performance of the RRUSS device including frame rate, resolution, spatial integrity, and motion tracking accuracy. To evaluate compatibility with radiation therapy workflow, we evaluated device-induced CT imaging artifacts, US tracking performance during beam delivery, and device compatibility with commercial radiotherapy planning software. The RRUSS device produced 4D volumes at 0.1-3.0 Hz with 60° lateral field of view (FOV), 50° maximum elevational FOV, and 200 mm maximum depth. Imaging resolution (-3 dB point spread width) was 1.2-7.9 mm at depths up to 100 mm and motion tracking accuracy was ≤ 0.3±0.5 mm. No significant effect of the RRUSS device on CT image integrity was found, and RRUSS device performance was not affected by radiotherapy beam exposure. Agreement within ±3.0% / 2.0 mm was achieved between computed and measured radiotherapy dose delivered directly through the RRUSS device at 6 MV and 15 MV. In vivo liver, kidney, and prostate images were successfully acquired. Our investigations suggest that a RRUSS device can offer non-interfering 4D guidance for radiation therapy and other diagnostic and therapeutic procedures.

A Monte Carlo study of the effect of an ultrasound transducer on surface dose during intrafraction motion imaging for external beam radiation therapy

“…The waterequivalent material employed in radiolucent probes should therefore produce similar results to those obtained in this study, however, have obvious advantages if left in place during planning CT imaging. 37 Small differences in the shape of the kV and MV dose perturbations were visible (see Fig. 6).…”

Ionizing radiation‐induced acoustics for radiotherapy and diagnostic radiology applications

“…While an array allows for 3D reconstruction of the dose distribution, the placement of transducers in such a geometry may be difficult due to radiation beam interference. However, it could be possible to account for transducers during the treatment planning stage, and a recent study demonstrated the construction and operation of a radiolucent transducer . Using a single transducer limits the amount of dosimetric information that can be extracted from detected acoustic signals, however, clinical implementation may become easier.…”

The Use of Ultrasound Imaging in the External Beam Radiotherapy Workflow of Prostate Cancer Patients

“…Second, the radiation can be delivered through the probe, but it requires that the possible dose deviations are taken into account during the treatment planning process, as investigated by, for example, Bazalova-Carter et al [ 76 ]. As a third solution, Schlosser and Hristov [ 77 ] designed a 4D radiolucent US probe with significantly less metal components close to the imaging field. This probe should produce a minimal interference with the radiation beam.…”